The Serie A side face Athletic Bilbao in a playoff over two legs, with the first match at their Stadio San Paolo next Tuesday.

A sellout attendance is expected for that game -- and after watching his side lose 2-1 in a home friendly against Paris Saint-Germain in front of a subdued crowd, Benitez urged them to step up their backing.

"But I know they will be important in helping our players when it matters, and the key against Athletic is going to be the stadium.

"Their fans are always positive and it's like playing against 12 men there -- so we've got to prove that our fans are even stronger."

Benitez said he was concerned about the test the opposition's fans and players would provide in Bilbao, saying: "Athletic have very strong players, and they've been playing together for years. The city gets behind them -- it will be tough."

Former Napoli striker Edinson Cavani was the cause of some of the reaction from the crowd against PSG, with the Uruguay international striker being booed by a section despite scoring over 100 goals in three seasons at the Serie A club.

He nevertheless thanked Napoli in a tweet after the game, saying he would "never forget the beautiful moments spent together with you."